Process for continuous production of membrane-electrode composites

ABSTRACT

A process for producing laminates which contain at least one centrally arranged, ion-conductive membrane which is, at least over a substantial part of its two mutually opposite flat faces, electrically conductively bonded to at least one catalytically active substance and to at least one two-dimensional, gas-permeable, electron-conductive contacting material, the bonding of at least two of the said components having been effected by lamination. The process comprises carrying out the bonding of the ion-conductive membrane, of the catalytically active substance and of the electron-conductive contacting material continuously. The ion-conductive membrane is brought together with at least the electron-conductive contacting material in the exact position by means of transport and feeding devices and the two components are laminated and bonded to one another by pressing them together. The range of variation in the a.c. resistances of the laminates produced by the process according to the invention is ±10%. The laminates are particularly suitable for use in fuel cells or electrolysers.

Fuel cells are electrochemical systems which can convert chemical energyinto electrical energy. Thus, a hydrogen/oxygen fuel cell converts thesegases into water with a release of electrical energy.

Fuel cells are composed of an array of a plurality of membrane/electrodeassemblies, separated by bipolar plates, a so-called stack, themembrane/electrode assemblies (MEA) in turn being constructed from twocatalytically active electrodes for the electrochemical conversion ofthe chemical substances and an ion-conductive electrolyte between theelectrodes for the charge transport. The bipolar plates serve toseparate the gas spaces and to connect the individual cellselectrically. Modern fuel cell designs operating at low temperatures donot contain any liquid electrolytes but conductive polymeric ionexchanger membranes (polymeric solid electrolytes).

The currently most promising production processes for membrane/electrodeassemblies are an impregnation process and a casting process, each ofwhich is followed by hot-pressing of the components.

In the impregnation process, a dissolved solid electrolyte is spread onthe electrode surface, or it is sprayed on as an emulsion by means of apressurized gas; it is capable of penetrating for a few micrometers intothe pore system. The prepared electrodes are then pressed with heatinguntil the electrode membrane fuses with them. Such a process forproducing membrane/electrode assemblies is described, for example, inU.S. Pat. No. 5,211,984, where a cation exchanger membrane is coatedwith a cation exchanger solution in which a platinum catalyst issuspended. This process is also known under the term “ink process”.

In casting, the dissolved solid electrolyte is mixed with the catalystmaterial and, if appropriate, a waterproofing agent, for examplepolytetrafluoroethylene (PTFE), to give a paste. This is either appliedfirst to a carrier or spread directly on the membrane and thenhot-pressed together with the latter, in order to minimize the contactresistances at the transitions between the membrane and the solidelectrolyte layers located in the paste or on the electrode.

A further process for producing electrode/membrane composites from anion exchanger material forming a core region and fuel cell electrodescontacted with both faces thereof is described in DE-C-4,241,150. Theion exchanger material is here formed from homopolymers or copolymerssoluble in a solvent and having at least one radical which candissociate into ions.

All preparation processes for gas diffusion electrodes with polymermembranes require a large number of in most cases manual working stepswhich are difficult to automate. Methods which are acceptable forexperiments on laboratory scale frequently lead in industrialmanufacture to insuperable obstacles, above all because of the highcosts.

Even though fuel cells are already in use in the space travel industry,a general commercial use in the automobile industry, for example, is notforeseeable in the near future, since the production costs, inparticular for membrane/electrode assemblies and the fuel cellsresulting from them, are several orders of magnitude above the costs forconventional internal combustion engines. Also for use in thedecentralized energy supply, the now available fuel cells are tooexpensive, for example as compared with oil heating and gas heating ordiesel generators.

For the use in a car, however, fuel cells in conjunction with anelectric drive represent a new drive concept which has some advantages.Thus, in the case of a fuel cell operated, for example, with hydrogenand oxygen, there is no pollutant emission at the vehicle, and theemission of the entire energy conversion chain is lower than in othervehicle drive systems. Moreover, the overall efficiency relative to theprimary energy is significantly higher. The use of fuel cells in theautomobile industry would make a noticeable contribution to thereduction of traffic-related pollutant emissions and the consumption ofenergy resources.

It is therefore the object to provide a process for producing laminates,in particular membrane/electrode assemblies suitable for use in fuelcells, which process allows the manufacture thereof in such a way thatthe production costs and the performance satisfy the requirements of theusers.

The present invention achieves this object by providing a process forproducing laminates, i.e. composites obtainable by bonding at least twocomponents, in particular membrane/electrode assemblies, which containat least one centrally arranged, ion-conductive membrane which is, atleast over a substantial part (>50%) of its two mutually opposite flatfaces, bonded to at least one catalytically active substance and to atleast one two-dimensional, gas-permeable, electron-conductive contactingmaterial, the bonding of at least two of the said components having beeneffected by lamination. The process comprises carrying out the bondingof the ion-conductive membrane, of the catalytically active substanceand of the electron-conductive contacting material continuously.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic drawing of a continuous lamination device.

FIG. 2 shows a schematic drawing of a catalyst coating device.

FIG. 3 shows a schematic drawing of an apparatus for continuouslaminating three webs followed by cutting.

FIG. 4 shows an optional insertion into the apparatus of FIG. 3.

FIG. 5 shows a net with discrete nonwoven pieces pressed thereon.

FIG. 6 shows the laminate of FIG. 5 with further processing.

FIG. 7a shows a top view of a segment cut from the laminate of FIG. 5.

FIG. 7b shows a side view of a segment cut from the laminate of FIG. 5.

FIG. 8 shows the product made by the apparatus of FIG. 3.

FIG. 9 shows a side view of a membrane/electrode assembly with a lateralgas seal.

FIG. 10 shows a laminate made by a comparative process.

The ion-conductive membrane is continuously brought together with atleast the electron-conductive contacting material, the membrane and/orthe contacting material being coated with a catalyst, in the exactposition by means of a transport and feeding device, and at least thesetwo components are laminated and bonded to one another by pressing themtogether on a roller arrangement (FIG. 1).

Examples of electron-conductive contacting materials which can be usedare all two-dimensional carbon fiber structures which possess anelectrical conductivity, preferably an electrical conductivity of >0.01Ωm, and have a porosity within their structure which permits an adequategas diffusion process.

In addition to composite materials which contain carbon in theconductive modification, however, metals, in particular stainless steel,nickel and titanium can also be used, preferably as powders, granules,papers, fibers, felts, nonwovens, fabrics, sintered plates orcombinations thereof, in particular two-dimensional mesh structures ofmetal or metal oxides of sufficient conductivity.

Structures are here especially preferred which, depending on the metalor metal oxide used, have a thickness in the range from 0.01 to 1 mm,preferably from 0.025 to 0.25 mm, and a mesh width in the range from0.001 to 5 mm, preferably 0.003 to 0.5 mm. In the case of carbonstructures, thicknesses in the range from 0.05 to 5 mm are preferred,especially from 0.1 to 2 mm. The weight per unit area of the carbonstructures is in this case in the range from 5 to 500 g/m², inparticular in the range from 20 to 150 g/m², and the porosity is in therange from 10 to 90%, preferably 50 to 80%.

In a preferred embodiment of the invention, graphitized two-dimensionalcarbon fiber structures are used. In particular the following contactingmaterials are used:

carbon fiber papers (for example ^(R)SIGRATHERM PE 204, PE 704, PE 715),carbon fiber fabrics (for example ^(R)SIGRATEX SPG 8505 and KDL 8023,KDL 8048), carbon fiber felts (for example ^(R)SIGRATHERM KFA 5 and GFA5), carbon fiber nonwovens (for example ^(R)SIGRATEX SPC 7011 and SPC7010 or TGP-H120 (Toray)) and composite carbon fiber structures (forexample ^(R)SIGRABOND 1001 and 1501 and 3001).

In a further development of the invention, the fibers and contact pointsof the fibers can additionally be coated with a layer of carbon in orderto increase the conductivity of the two-dimensional carbon fiberstructure.

A variant for producing such a two-dimensional fiber structure comprisesthe use of polyacrylonitrile fabrics and nonwovens which have beenconverted directly into the carbonized/graphitized form via a specialdirect oxidation process, so that the expensive detour via the processof producing individual filaments and the subsequent further processingto give two-dimensional fiber structures can be by-passed (German PatentApplication P 195 17 911.0).

Materials of particular interest for the ion-conductive membrane aregenerally those which show properties of the solid state in one part oftheir structure and those of the liquid state in another part, and arethus dimensionally very stable but also conduct protons very well.Polymers suitable for this purpose are those which have a radical whichcan dissociate into ions. Preferably, cation-conductive membranes areused. The ion conductivity for protons is preferably 0.5 to 200 mS/cm,especially 5 to 50 mS/cm. The membrane thickness is preferably in therange from 0.1 μm to 10 mm, in particular from 3 μm to 1 mm. Moreover,it must be ensured in the processing of the polymers to give themembrane, that the latter is gas-tight.

The base materials for the ion-conductive membrane can be homopolymersand copolymers or mixtures thereof, which can be obtained as viscoussolutions or dispersions with suitable liquids and can be processed togive membranes. If mixtures are used, at least one component of themixture must be ion-conductive, while other components of the mixturemay indeed be insulators for the ion conductivity which, however, on theother hand, confer, for example, certain mechanical properties or ahydrophobic character to the membrane.

In particular, polymers can be used which have a high mechanicalstability, a high temperature resistance and an adequate resistance ofchemicals for the use as a membrane material in electrochemical cells.

Polymers which can be used according to the invention are described in,for example, DE-C-4,241,150, U.S. Pat. No. 4,927,909, U.S. Pat. No.5,264,542, DE-A-4,219,077, EP-A-0,574,791, DE-A-4,242,692; DE-A-19 50027 and DE-A-19 50 026 and in DE-A-19 52 7435. These specifications areincorporated herein by reference.

Polymers with dissociable groups are preferably used as ion-conductivematerials for the membrane which can be employed according to theinvention. The dissociable groups can either be covalently boundfunctional groups (for example —SO₃M, —PO₃MM′, COOM and others (M,M′=H,NH₄, metals)) or acids which are present as swelling agents in thepolymer (for example H₃PO₄ or H₂SO₄). Preferred are polyarylenes withcovalently bound dissociable groups, fluorinated polymers withcovalently bound dissociable groups or basic, acid-swollen polymers witharyl rings. Particularly preferred polyarylenes have, as the main chain,a polyarylether-ketone, a polyarylether-sulfone, a polyaryl sulfone, apolyaryl sulfide, a polyphenylene, a polyarylamide or a polyaryl ester.Likewise particularly preferred are polybenzimidazoles (PBI), containingdissociable acid groups (for example PBI swollen with H₃PO₄). Mixturescontaining at least one of the abovementioned polymers are alsosuitable.

In a further preferred embodiment, completely fluorinated polymers canalso be present, i.e. those which contain C—F bonds in place of C—Hbonds. These are very stable against oxidation and reduction and are insome ways related to polytetrafluoroethylene. It is particularlypreferred when such fluorinated polymers also contain water-attracting(hydrophilic) sulfonic acid groups (SO₃H) in addition to thewater-repellent (hydrophobic) fluorine groups. These properties arepresent, for example, in the polymers known under the brand name^(R)Nafion.

Polymers of this type are, in their swollen state (caused by the waterabsorption), relatively stable dimensionally due to their hydrophobic,solid-like skeleton, on the one hand, and show very good protonconductivity in their hydrophilic, liquid-like regions, on the otherhand.

Catalysts which can be used for the production of membrane/electrodeassemblies by the process according to the invention are generally allelectrochemical catalysts which catalyze the redox reactions 2H₂/4H⁺ andO₂/2O²⁻. These substances are in most cases based on elements of the 8thsubgroup of the Periodic Table, it being possible for substances to beadditionally present which are based on elements from other groups ofthe Periodic Table. Those metals or compounds thereof are also usedwhich catalyze the conversion of methanol and water to carbon dioxideand hydrogen at low temperatures. In particular, metals, oxides, alloysor mixed oxides of these elements are used as catalysts.

The gas-permeable, electrically conductive structure serving aselectrode can be converted by coating with the catalyst into the activeform which ensures the electrical contact. Generally, both theion-conductive membrane and the electron-conductive contacting materialor both can be coated with the catalyst by the process according to theinvention. The catalyst concentration of the ion-conductive membrane oron the contact material is usually in the range from 0.001 to 4.0mg/cm², the upper limit of the catalyst concentration being given by thecatalyst price and the lower limit given by the catalytic activity. Theapplication and bonding of the catalyst take place according to theknown processes.

Thus, for example, it is possible to coat the contacting material with acatalyst suspension containing the catalyst and a solution of the cationexchanger polymer. The cation exchanger polymers can generally be allthe ion-conductive polymers mentioned above.

Preferably, metals or alloys of metals selected from the 1st, 2nd and8th subgroup of the Periodic Table and also Sn, Re, Ti, W and Mo areused as catalytically active materials, in particular Pt, Ir, Cu, Ag,Au, Ru, Ni, Zn, Rh, Sn, Re, Ti, W and Mo. Further examples of catalystswhich can be used according to the invention are platinum, gold,rhodium, iridium and ruthenium catalysts applied to support materials,for example ^(R)XC-72 and ^(R)XC-72R made by E-TEK.

The catalyst can be deposited on the material to be coated by a chemicalreaction (DE-A-4,437,492.5). Thus, for example, it is possible toimpregnate the membrane and/or the contacting material withhexachloroplatinic acid and to deposit elemental platinum by using areducing agent, for example hydrazine or hydrogen (JP 80/38,934).Platinum can be applied from an aqueous solution which preferablycontains (Pt(NH₃)Cl₂) (U.S. Pat. No. 5,284,571).

Examples of further possibilities for bonding the catalyst aresputtering, the CVD process (chemical vapor deposition), cold plasmadeposition, the physical vapor deposition process (PVD), electron beamvaporization and electrochemical deposition on the material to becoated. Furthermore, an activation of rare metals can be effected viaion exchange on oxidatively modified carbon blacks and subsequentreduction.

Coating of the two-dimensional fiber structure with a catalystsuspension, which already contains the catalyst as such, for examplemetallic platinum, has proven to be particularly appropriate in theprocess according to the invention. In particular with a view to uniformdistribution of the catalyst component and the later bonding of theelectrode structure to the cation exchanger membrane, considerableadvantages result.

For example, a blade arrangement in combination with a hot roller(FIG. 1) or an application device such as is known from continuousprepreg fabrication are suitable for applying the suspension of activelyeffective catalyst.

The fiber structure thus impregnated, which is the so-called gasdiffusion electrode, can then be wound up or fed directly in ribbon formto the continuous process for producing a membrane/electrode assembly(MEA).

Both the surface quality of the ion-conductive material and the fixingof the catalyst suspension can be influenced by a preceding dippingbath. The open pore volume of the two-dimensional fiber structure andthe bonding to the phase boundary on the one hand and the adhesive powerfor the bonding of the catalyst suspension on the other hand can beadjusted by the selection of suitable adhesion promoters and binders aswell as fillers (FIG. 1 and FIG. 2). In this step, advantageously anarrangement of a vacuum belt filter followed by a controllable dryingsection is used.

The consistency/degree of drying of the applied catalyst suspension canthen be adjusted such that a subsequent lamination can be carried out inan optimum manner.

If the gas diffusion electrode should first be rolled up before it isprocessed further, sticking of the electrode to itself can be preventedby the selection of a suitable separating paper which is wound uptogether with it.

The electron-conductive contacting material is then continuously broughttogether with the ion-conductive membrane in the exact position, and theion-conductive membrane is then laminated and bonded on at least one ofits flat faces to the contacting material on a roller arrangement.

In a variant according to the invention, the contacting material can, ifit is laminated to both flat faces of the ion-conductive membrane,contain a different catalyst for each face of the membrane. In additionto the ion-conductive membrane, two contacting materials, which may becomposed of different materials, can also be used as starting materials.

In an alternative embodiment, the electron-conductive contactingmaterial can first be continuously coated and laminated in each case toone face of the ion-conductive membrane, and these two coated halfcomponents (half membrane/electrode assemblies) are then, after wettingor incipient dissolving of the ion-conductive surface, fitted togetherand laminated by pressing them together to give a membrane/electrodeassembly. In this variant again, either half membrane/electrodeassemblies comprising components made of the same materials, i.e. thesame electron-conductive contacting material and ion-conductive membranecomposed of the same polymer, or half membrane/electrode assemblies ofdifferent composition, i.e. a different ion-conductive membrane and/or adifferent contacting material and/or a different catalyst, can be used.

In order to improve the adhesion between the membrane and the contactingmaterial, the membrane can, if appropriate, be at least partiallyplasticized before the lamination process either by swelling in anon-solvent, for example water, acetone, methanol or another aliphaticalcohol, or by swelling in mixtures of a solvent, preferably apredominantly polar aprotic solvent, for example N-methylpyrrolidone(NMP), dimethyl sulfoxide (DMSO), dimethylformamide, g-butyrolactone, orprotic solvents such as, for example, sulfuric acid or phosphoric acidor a non-solvent.

Moreover, to improve the adhesion and to bond the components, thecontacting material or at least one flat face of the membrane or bothcomponents can be incipiently dissolved, wetted or incipiently swollenby a solvent or by a polymer solution, and the components, i.e. one orboth flat faces of the ion-conductive membrane and at least oneelectron-conductive contacting material, can then be fitted together bypressing and bonded by lamination.

The coating of the components can be carried out either with puresolvent or with a polymer solution, in which case the polymerconcentration can amount to 0 to 100% by weight, preferably 5 to 50% byweight. Polymers which can be used for the preparation of the coatingsolutions are the abovementioned ion-conductive polymers. Preferably, apolymer solution of the polymer forming the ion-conductive membrane isused for coating. The coating is applied particularly in a layerthickness from 1 to 200 μm, especially 5 to 100 μm. In this case, eitherthe contacting material or at least one of the flat faces of theion-conductive membrane can be coated with a catalytically activesubstance. In a further variant according to the invention, the catalystcan be present in the coating material promoting adhesion, i.e. in thesolvent or in the polymer solution which is to be applied.

The coating or so-called conditioning of the ion-conductive membranetakes place via a slot die, if an application of solvent or polymersolution to one face is concerned. Suitable slot dies according to theinvention are dies having a width in the range from 0.1 to 5 m and aslot width in the range from 10 to 1000 μm.

For coating, the membrane is taken past the slot die either in thehorizontal direction (above or below the die) or in the verticaldirection (ascending or descending). In the case of conditioning on bothfaces of the membrane, the application of the solvent or polymersolution can be carried out correspondingly by passing the membranethrough by means of two slot dies or by conditioning of the membrane ina dipping bath which contains the solution to be coated.

Alternatively, the membrane can be coated by taking it past a blade. Thewidth of the blade is preferably in the range from 0.1 to 5 m with aslot width in the range from 5 to 500 μm. The ribbon speed is in thiscase especially between 0.5 mm/second and 10 m/second, preferably 5mm/second to 1 m/second.

For lamination, the individual components, i.e. at least oneelectron-conductive contacting material and at least one ion-conductivemembrane, are brought together by means of feeding and positioningdevices and laminated to one another between pairs of rollers or in apress. Preferably, the contacting material and/or the ion-conductivemembrane are brought together as two-dimensional structures andlaminated at a temperature in the range from 5 to 300° C., especially 25to 200° C., and a suitable contact pressure, preferably in the rangefrom 10⁷ to 10¹² Pa, especially 10⁸ to 10¹⁰ Pa. It is to be noted herethat the contact pressure in the case of using rollers is frequentlygreatly dependent on the shape and size of the rollers. By means of thislamination process, the electrode structure is pressed directly into theupmost incipiently dissolved or incipiently molten layer of theion-conductive membrane.

The production of a composite electrode membrane from two halfmembrane/electrode assemblies is correspondingly effected by incipientlydissolving the ion-conductive membrane of one or both halfmembrane/electrode assemblies with a solvent or polymer solution,positioning and feeding the two assemblies to the pairs of rollers andlamination thereof to give a complete membrane/electrode assembly.

The diameter of the pairs of rollers used according to the invention ispreferably in the range from 0.1 to 2 m.

In a special embodiment, the ion-conductive membrane can be laminated toa contacting material which has already been cut into ready-to-use unitsadapted to the intended later use, for example in the form of pieces ofcarbon nonwoven whose shape and size correspond to the carbon nonwovensused in a fuel cell. According to the invention, the units can beunrolled in such a way that the distance between the units correspondsto twice the width of the uncoated membrane rim, required in a fuelcell, preferably 0.1 to 100 mm, especially 1 to 50 mm. The advantage ofthis process variant according to the invention is above all a saving ofprocess steps during the subsequent further processing of the resultingmembrane/electrode assemblies to give fuel cells.

The laminates of electron-conductive contacting material, catalyst andion-conductive membrane obtained by the continuous process according tothe invention are freed from still adhering superfluous components in acontinuous stage downstream of the lamination and coupled thereto.

One possibility for such a conditioning comprises, for example, passingthe laminate in ribbon form through a drying section, for example acirculating air oven, heated to 10 to 250° C., especially 20 to 200° C.In this way, still adhering solvent residues or water are evaporated. Ina particular embodiment, there can be a temperature gradient in thedrying section along the direction of motion.

A further possibility for removing the volatile constituents comprisesdrying the laminate by means of infrared radiation, in particular incombination with a downstream circulating-air dryer.

In a further process variant, the removal of the superfluous, stilladhering components can take place in a downstream washing step. Thus,for example, still adhering solvents or non-solvents or polymercomponents can be extracted by a liquid which does not dissolve themembrane-forming polymers. For example, water/NMP mixtures and mixturesof NMP and lower aliphatic alcohols are used here. The NMP content isthen preferably below 25%. In particular, the extraction in this varianttakes place by spraying the laminate with the liquid or by passing thelaminate ribbon with the aid of deflection rollers through anappropriate dipping bath. After the extract has dripped off, thelaminate is subjected to a subsequent drying process. The drying of thelaminate can be carried out as described above.

In order to bring the laminate obtained by the process according to theinvention already into a form suitable for incorporation in a fuel cell,a so-called finishing step can follow the conditioning stage as afurther process step.

In this case, the laminate present as a ribbon can be divided atappropriate regular distances adapted to the further intended use bymeans of suitable cutting or punching machines. If pieces of carbonnonwoven have already been used as contacting material in the productionof the laminate, the laminate ribbon is cut up in the uncoated regions,so that the pieces of laminate thus obtained are coated only in thecentral region, but not at the rim.

Moreover, it is possible to apply self-curing sealing materials to theouter, uncoated or to the coated rim zone of the laminate in asubsequent coupled step, so that the contacting material is no longergas-permeable (U.S. Pat. No. 5,264,299). In particular, curable siliconeresins can here be used as sealing materials, which are applied in aliquid form and fully cure spontaneously. During the subsequentincorporation of the laminate or of the membrane/electrode assembly intoa fuel cell, the sealing material thus applied serves for lateralsealing of the cell and for preventing egress of fluids and the outflowof fuel gases or oxidizing gases.

A determination of the a.c. resistances can provide information aboutthe reproducibility of the production of the laminates. In the case oflaminates from one batch, the resistance also correlates to the power,but not between different laminates. Laminates produced by the knowndiscontinuous processes show a.c. resistances which vary between 10 mΩand 10 Ω. The products thus obtained frequently contain distortions, airinclusions or similar defects. By contrast, the continuous processaccording to the invention leads to uniform bonding of the electrodestructure to the ion-conductive membrane and regularly to laminateshaving a range of variation of ±10%, especially ±5% (measured in theready-to-operate state). The resistances of the membrane/electrodeassemblies obtained by the process according to the invention areusually in the range from 0.02 to 0.6 Ω, in particular in the range from0.04 to 0.45 Ω. Using the process according to the invention, laminates,in particular membrane/electrode assemblies and/or composite electrodemembranes, can be produced in a simple, economical and easilyreproducible manner. Therefore, and owing to their low a.c. resistances,they are especially suitable for incorporation into fuel cells andelectrolysis.

The invention is explained in more detail below by reference toexemplary embodiments and to the attached figures.

EXAMPLES Example 1

Membrane material (FIG. 3, 1): Sulfonated polyarylether-ketone of theformula (1), prepared according to EP 0,574,791, ion exchangerequivalent 1.4 mmol/g, thickness 100 μm, roll form, width 400 mm.

Coating material (FIG. 3, 3): Mixture composed of

15 g of sulfonated polymer identical to the membrane material,

15 g of platinum catalyst (30% of Pt/Vulcan XC-72, made by E-TEK, Inc.Natick, USA),

70 g of N-methylpyrrolidone.

Carbon fabric (FIG. 3, 4): VP 676, made by SGL Carbon GmbH, Wiesbaden,Germany. The membrane (1) is passed through between two slot dies (2)(width of the die 370 mm, slot width 500 μm) at a speed of 5 mm/second;during this, a coating (3) of 100 μm thickness is applied to both facesof the membrane. Downstream of the slot dies, carbon fabric (4) is shotin on both sides via two rollers (5) (width 450 mm, diameter 200 mm), sothat a laminate is formed. The upper roller exerts a force of 1000 N onthe laminate running underneath. The laminate in the form of a ribbon ispassed through a two-chamber oven (6) (length 3 m), in which the NMP isremoved from the coating material (3). The first chamber (length 1 m) isheated to 120° C., the second chamber (length 2 m) is heated to 80° C.Downstream of the oven, the laminate is divided into pieces (8) bycontinuously operating parallel sheers (7); the width of the pieces isgiven by the width of the laminate ribbon, and the length of the piecesis 500 mm. The laminate thus obtained can be incorporated as amembrane/electrode assembly into a membrane fuel cell and delivers therein hydrogen/oxygen operation (each at 2 bar and 80° C.) a maximumelectric power of 3.1 kW/m².

Example 2

Variant to Example 1. After the carbon fabric (FIG. 3) has been rolledon, the laminate is introduced via a deflection roll (diameter 1 m) intothe apparatus sketched in FIG. 4 at the point marked A. Water (25m/second) is sprayed through two nozzle heads (9) onto both sides of themembrane, the water extracting NMP out of the coating. 0.5 m below thenozzle heads, there are outflow troughs (10) for the sprayed-on water onboth sides of the laminate ribbon. The laminate is then passed via adeflection roll into the oven (6) (both chambers at 80° C.; downstreamof the oven, there are additionally in each case two commerciallyavailable 150 W IR-lamps 100 mm above and below the laminate) andfurther treated as in Example 1. The laminate thus obtained can beincorporated as a membrane/electrode assembly into a membrane fuel celland delivers there in hydrogen/oxygen operation (each at 2 bar, 80° C.)a maximum electric power of 3.8 kW/m².

Example 3

For the following embodiment, a laminate of a commercially availablecarbon nonwoven (TGP-H-120, made by Toray, Tokyo, Japan), which has beencoated with 40 g/m² of platinum by sputtering, and of a commerciallyavailable polyethylene net is used. The carbon nonwoven is pressed inindividual pieces (11) (80 mm×120 mm) onto the net (12), so that thedivision sketched in FIG. 5 results, in which the carbon nonwoven piecesare separated from one another by gaps. The side sputtered with platinumfaces away from the side laminated with the polyethylene net

The laminate is used in Example 2 in place of the carbon fabric. Bycontrast to Example 2, the coating solution does not, however, containany catalyst. The laminate is contacted via the carbon nonwoven sidewith the membrane. The resulting laminate consists of a membrane (13)which is provided on both faces with isolated carbon fabric pieces (14).Using a combination of continuously operating shears (commerciallyavailable perforation tools), this laminate is cut along the lines (15).This gives laminate pieces (FIG. 7) whose rim (16) represents only afreestanding membrane and which are coated inside of the rim withcatalyst-containing carbon fabric (17). These pieces are particularlysuitable as membrane/electrode assemblies for stacking in membrane fuelcells, because the freestanding and smooth rim can be sealedgas-tight—if necessary with the use of conventional, elastic gaskets.The laminate is incorporated as a membrane/electrode assembly into amembrane fuel cell and delivers there in hydrogen/oxygen operation (eachat 2 bar, 80° C.) a maximum electric power of 2.9 kW/m².

Example 4

A laminate obtained according to Example 1 is imprinted with a siliconerubber solution (Sylgard™, DOW) in an industrially usual, continuouslyrunning gravure printing process. The printing unit is integrateddirectly downstream of the oven and produces on the laminate a grid(FIG. 8) of gummed areas (18) in which the carbon fabric is fullyimpregnated with silicone rubber. By means of a combination ofcontinuously operating shears (commercially available perforationtools), this laminate is cut along the lines (15). In this way,membrane/electrode assemblies with an integrated, lateral gas seal (18)are obtained (FIG. 9).

Example 5

Comparison experiment with Example 1. Membrane material, coatingmaterial, carbon fabric and quantitative data as Example 1.

Procedure: Membrane material 19 (200×200 mm²), coating material (20)(180×180 mm², applied by box-type blade) and carbon fabric (21) (180×180mm²) are pressed to one another as shown in FIG. 10 (p=10⁹ Pa, t=30minutes, T=80° C.).

Determination of the a.c. resistance of laminates: For the measurement,the laminate is clamped in between the two halves of a steel block witha cylindrical bore of 40 mm diameter. This bore is lined with steelmats. The topmost steel mat protrudes by 0.2 mm from the bore. The meshwidth of the mat is 0.5 mm. The electrodes protrude by 5 mm beyond theedge of the steel mat. In this case, the conditions of the test fuelcell are simulated, and the MEA is incorporated in the ready-to-operatestate in order to adapt the conditions to the test fuel cell. After thelaminate has been clamped in between the halves of the steel block,these were pressed together by means of screws having an M12 thread. Foruniform loading, washers are inserted as springs between the steel blockand nuts. Before the nuts are tightened, a square-wave voltage of 1 kHzis applied to the laminate for a measurement of the a.c. resistance. Themeasuring voltage (as V_(SS)) is in the range below 12 volts. For themeasurement, a Voftcraft LCR measuring instrument of type 4090 is used.The nuts are then slowly tightened crosswise until there is no longerany noticeable change in the a.c. resistance. The final resistance isread off after a balancing phase of 3 minutes. The deviation of the a.c.resistances of the laminates produced according to the invention is inthe range of <10%, especially <5%.

What is claimed is:
 1. A process for producing laminates which containone centrally arranged, ion-conductive membrane which is, at least overa substantial part of at least on of its two mutually opposite flatfaces, electrically conductively bonded to at least one catalyticallyactive substance and to at least one two-dimensional, gas-permeable,electron-conductive contacting material, the bonding of at least two ofthe said components having been effected by lamination, which comprisescarrying out the bonding of the ion-conductive membrane, of thecatalytically active substance and of the electron-conductive contactingmaterial continuously.
 2. The process as claimed in claim 1, where inthe ion-conductive membrane is brought together with at least theelectron conductive contacting material in the exact position by meansof transport and feeding devices and at least the two components arelaminated and bonded to one another by pressing them together.
 3. Theprocess as claimed in claim 1, wherein the lamination is effected bymeans of rollers exerting a pressure.
 4. The process as claimed in claim1, wherein the ion-conductive membrane and/or the contacting materialis/are fed and processed in ribbon form.
 5. The process as claimed inclaim 1, wherein the electron-conductive contacting material and/or atleast one of the flat faces of the ion-conductive membrane is/are coatedwith a catalytically active substance.
 6. The process as claimed inclaim 1, wherein a cation-conductive membrane is used as theion-conductive membrane.
 7. The process as claimed in claim 1, whereinthe ion-conductive membrane is used as a membrane which contains apolymer from the group comprising the polyarylether-ketones, polyarylenesulfides, polyarylether-sulfones, poly-(1,4-phenylene)s andpolybenzimidazoles or from the group comprising the sulfonatedpolyaramides or a completely fluorinated polymer.
 8. The process asclaimed in claim 1, wherein the catalyst used is a platinum, gold,rhodium, iridium or ruthenium catalyst.
 9. The process as claimed inclaim 1, wherein the electron-conductive contacting material used is atwo-dimensional carbon fiber structure from the group comprising carbonpaper, carbon nonwoven, carbon fabric, carbon felt or composite carbonfiber structures or metals.
 10. The process as claimed in claim 9,wherein the contacting material used is a two-dimensional graphitizedcarbon fiber structure.
 11. The process as claimed in claim 9, whereinthe contacting material used is a two-dimensional carbon fiber structurewhose fibers and contact points of the fibers are additionally coatedwith a layer of carbon.
 12. The process as claimed in claim 1, whereinthe ion-conductive membrane is laminated on at least one of its flatfaces to an electron-conductive contacting material.
 13. The process asclaimed in claim 12, wherein the ion-conductive membrane is bonded to adifferent contacting material on each of its flat faces.
 14. The processas claimed in claim 12, wherein the ion-conductive membrane is laminatedon both of its flat faces to an electron-conductive contacting materialcarrying a catalyst, the contacting material for one face of themembrane carrying a catalyst which is different from that carried by thecontacting material for the other face of the membrane.
 15. The processas claimed in claim 12, wherein the membrane/electrode assembly isproduced by bonding two laminates, each composed of an ion-conductivemembrane and an electron-conductive contacting material, by laminationat the ion-conductive surfaces.
 16. The process as claimed in claim 1,wherein, for bonding the components, the electron-conductive material orat least one flat face of the membrane or both components arecontinuously coated with a solvent or a polymer solution.
 17. Theprocess as claimed in claim 16, wherein the adhesion-promoting coatingmaterial contains the catalyst.
 18. The process as claimed in claim 16,wherein a polymer solution, which contains the membrane-forming,ion-conductive polymer, is used for coating.
 19. The process as claimedin claim 1, wherein the components which are to be laminated are broughttogether in the intended manner by means of feeding and positioningdevices and are laminated at a temperature in the range from 5 to 300°C.
 20. The process as claimed in claim 1, wherein the components whichare to be laminated are brought together in the intended manner by meansof feeding and positioning devices and are laminated at a pressure inthe range from 10⁷ to 10¹² Pa.
 21. The process as claimed in claim 1,wherein the laminates obtained are freed of still adhering, superfluousconstituents in a continuous stage downstream of the lamination andcoupled thereto.
 22. The process as claimed in claim 21, wherein thelaminate is passed through a heated drying section at a temperature inthe range from 10 to 250° C.
 23. The process as claimed in claim 21,wherein the superfluous constituents are removed in a downstream washingstep and the laminate is subsequently dried.
 24. The process as claimedin claim 1, wherein, in a continuous stage downstream of the lamination,sealing materials are applied to the outer rim zones of the laminate,along which a seal against fluids and gases is necessary during lateruse.
 25. The process as claimed in claim 1, wherein the laminate isdivided in a process downstream of the lamination at correspondingdistances which are adapted to the intended further use.
 26. A laminateproduced by a process as claimed in claim 1, wherein the range ofvariation of the a.c. resistance of the laminates of one series is +10%.27. A laminate as claimed in claim 26, which is a membrane/electrodeassembly.
 28. The use of a laminate produced as claimed in claim 1 infuel cells or electrolysers.